One of the main problems which occurs in hydraulic engineering is the corrosion of metals in both treated and untreated cooling water systems. The corrosion of metals such as steel, aluminum, brass and copper, which are commonly found in water systems, is primarily due to dissolved oxygen and carbon dioxide. Materials which remove oxygen, such as sodium sulfite or hydrazine, are not economical and are technically inadequate. Hence, Zn.sup.++, chromates, molybdates, polyphosphates, ortho-phosphate, and organo-phosphonates are added to cooling water to form protective films on metal surfaces. Chromates are very efficient corrosion inhibitors. However, they are often environmentally undesirable due to the well known toxic effects. Zn.sup.++ has similar environmental problems and it also has low solubility products with ortho phosphate, hydroxide and carbonate, which products can form sludge and deposits responsible for promoting corrosion. Polyphosphates are not as efficient as chromates and they are unstable in a cooling water environment; thus, they decompose by hydrolysis to ortho and pyro-phosphates which often cause sludge and deposits. Ortho-phosphates are not as efficient as chromates and, if they are not controlled properly, can also form sludge and deposits. Although organo-phosphonates provide some corrosion protection, they are not nearly as efficient as chromates.
In addition to the problem of metal corrosion, cooling water systems can deposit materials, such as calcium carbonate and calcium phosphate, on metal so as to form a scale thereon. Such scaling adversely affects heat transfer properties and liquid velocities in the cooling systems.
Therefore, it is an object of this invention to provide an improved method for treating aqueous systems, e.g., cooling water systems, which method efficiently provides a high level of protection against metal corrosion and the formation of scale.